As it is known by the man skilled in the art, ablation of a chosen tissue part, such as a tumor (for instance a liver tumor (both primary and metastases) or a renal tumor or else uterine fibroids), can now be done in a minimally invasive way by an operator (generally a surgeon, a radiologist, or an interventional radiologist) by means of a remotely controllable needle coupled to an array of heating tines which can be deployed from the needle with the assistance of real time images displayed onto a screen for placement guidance.
In order to ablate a chosen tissue part, one may acquire image data in the area comprising this chosen tissue part to display real time images of this area onto a screen, then one may position the needle and deploy the heating tines near the chosen tissue part with the assistance of the displayed real time images, and finally one may heat the tissues near the chosen tissue part by means of the heating tines at a temperature which is adapted for inducing cell destruction into the chosen tissue part.
For instance, the tissue heating can be performed by a radiofrequency (RF) excitation through the heating tines. In this case, the ablation technique is called RadioFrequency Ablation (or RFA). This type of ablation method is notably described in the patent documents U.S. Pat. No. 7,025,767 and US 2003/0208197.
In case of an RFA technique the assistance (or guidance) through ultrasound (or echoes) images is widely used because it offers spatial and temporal advantages over other techniques of image acquisition such as computed tomography (or CT) and magnetic resonance imaging (or MRI).
In order for the above mentioned ablating method to be effective, the array of tines must be deployed uniformly in angle and could also possibly curve back. But, due to inhomogeneities in tissues and vessels (including in tissue and vessel stiffness), actual heating tine deployment is often not uniformly accomplished, which produces cold spots that do not allow local ablations, and/or induces flattening of heating tines, which produces a more pyramidal treatment volume instead of a desired spherical or toroidal shaped volume.
To improve the heating tine deployment it is mandatory to precisely visualize the margins of the tissue part to be ablated and the array of heating tines, and therefore the relative positions of the heating tines with respect to the tissue part to be ablated. But the visualization of the heating tines appears to be difficult, notably with a conventional B-mode ultrasound technique, due to the size of the heating tines and the brightness of the surrounding tissues (a portion of a heating tine or of a subset of heating tines can be visualized if it is well oriented relative to the ultrasound beam).
For instance, in case of an RFA method one often uses temperature or electrical impedance measurements of the tines to determine RFA efficiency and determine when RFA is complete. But, when the deployment is partly incorrect, ablation errors may occur, resulting in smaller-than-desired ablation areas and thus incomplete treatment of desired tumor-region ablation.
So, the object of this invention is to produce images of an area showing the relative positions of heating tines with respect to a chosen tissue part, for instance to improve the positioning of these heating tines, and hence to improve the efficiency of an ablation technique and to reduce the occurrence of errors.